Vehicles such as cars incorporate a structural skeleton designed to withstand all loads that the vehicle may be subjected to during its lifetime. The structural skeleton is further designed to withstand and absorb impacts, in case of e.g. collisions with other cars.
The structural skeleton of a car in this sense may include e.g. a bumper, pillars (A-pillar, B-Pillar, C-Pillar), side impact beams, a rocker panel, and shock absorbers. These components may incorporate a beam and additional plates around such a beam. It is known to use beams having a substantially U-shaped (or “hat”-shaped cross section). Such beams may be manufactured in a variety of ways, and may be made of a variety of materials.
For the structural skeleton of a car, or at least for a number of its components, it has become commonplace in the automotive industry to use so-called ultra-high strength steels (UHSS), which exhibit an optimized maximal strength per weight unit and advantageous formability properties.
Some of these steels, such as e.g. 22MnB5 steel, are designed to attain a microstructure after heat treatment, which confers good mechanical properties and makes them especially suited for the hot stamping process used to form steel blanks into particular automobile parts. In order to avoid the decarburization and the scale formation during the forming process, 22MnB5 is presented with an aluminum-silicon coating. Usibor® 1500P, commercially available from Arcelor Mittal, is an example of a steel used in various components, possibly involving so-called tailored and patchwork blanks.
Usibor® 1500P is supplied in ferritic-perlitic phase. It is a fine grain structure distributed in a homogenous pattern. The mechanical properties are related to this structure. After heat treatment during hot stamping process, a martensite microstructure is created. As a result, maximal strength and yield strength increase noticeably.
A typical hot stamping process may include heating a blank of flat steel in a furnace to an austenitic state and hot forming the blank between a cooled pair of tools (e.g. in a die). The blank may be maintained between the tools until the blank has hardened and has rapidly cooled down. An essentially martensitic structure with a tensile strength of more than 1.300 Mpa, e.g. approximately 1.500 Mpa can be obtained.
The use of beams having a relatively thin-walled U-shaped cross-section may be advantageous since they can be manufactured using e.g. hot stamping processes and because they provide good bending stiffness per unit weight and thus enable improved performance under bending and in compression. As mentioned before, in some implementations, additional platework may be provided, e.g. a cover plate “closing” the U-shaped cross-section. Such a closed cross-section may improve stiffness of the resulting component.
In examples of the present disclosure, beams having a substantially U-shaped cross-section with improved properties are provided.